The Small Heath is generally considered a common butterfly occurring throughout Britain and Ireland in open short grassland where fine grasses grow. However it has become rather less common than it used to be in many areas in recent decades. (For further details on this species see http://www.butterfly-conservation.org/).

Status details : Status since 1976 is Rapid decline with a decrease of -58.1%Status over the last 20 years is Stable with a increase of 7%Status over the last 10 years is Stable with a decrease of -4.9%

Log collated index plot

This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in
populations from year to year, and is scaled so that the average index over the whole series is equal to 2
(horizontal line). For greater detail about how this index is derived, click on the green question mark above.

Trend description :The trend for this species shows a significant decline over the monitoring period and the Small Heath is now listed as a UK BAP priority species. High numbers have tended to be in years of warmer summers indicating the importance of good summer temperatures for this species. The biggest declines have tended to be on woodland transects where the combination of increasing shade and eutrophication have probably been the main operative factors. In fact at many woodland sites the Small Heath appears to have become extinct. Open grassland sites have generally fared better (but by no means all) and there have been significant increases at a few sites.

Phenology plot

Phenology plot

This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.

This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.

Coverage

In total, Small Heath has been recorded from 712 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 841 sites, with an average index of 60 individuals per site.

For 433 of these sites, Small Heath has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.

In 2017, 34177 individuals were recorded from 394 sites, producing annual indices at 307 of these.

This map shows the trend in abundance at particular transect sites for which data has been received within the last five years. Trends (increasing, declining or stable) are assessed at sites where the species has more than five years of annual index data. Use the option boxes below to view plots for individual sites.